000204383 001__ 204383
000204383 005__ 20181203023726.0
000204383 0247_ $$2doi$$a10.1021/ja077749v
000204383 022__ $$a0002-7863
000204383 02470 $$2ISI$$a000255629400027
000204383 037__ $$aARTICLE
000204383 245__ $$aDynamics of silica-supported catalysts determined by combining solid-state NMR spectroscopy and DFT calculations
000204383 260__ $$bAMER CHEMICAL SOC$$c2008
000204383 269__ $$a2008
000204383 336__ $$aJournal Articles
000204383 520__ $$aThe molecular dynamics of a series of organometallic complexes covalently bound to amorphous silica surfaces is determined experimentally using solid-state nuclear magnetic resonance (NMR) spectroscopy and density functional theory calculations (DFT). The determination is carried out for a series of alkylidene-based catalysts having the general formula [( SiO)M(ER)(=CHtBu)(R')] (M = Re, Ta, Mo or W; ER = CtBu, NAr or CH(2)tBu; R' = CH2tBu, NPh2, NC4H4). Proton-carbon dipolar coupling constants and carbon chemical shift anisotropies (CSA) are determined experimentally by solid-state NMR. Room-temperature molecular dynamics is quantified through order parameters determined from the experimental data. For the chemical shift anisotropy data, we validate and use a method that integrates static values for the CSA obtained computationally by DFT, obviating the need for low-temperature measurements. Comparison of the room-temperature data with the calculations shows that the widths of the calculated static limit dipolar couplings and CSAs are always greater than the experimentally determined values, providing a clear indication of motional averaging on the NMR time scale. Moreover, the dynamics are found to be significantly different within the series of molecular complexes, with order parameters ranging from <S-z> = 0.5 for [( SiO)Ta(=CHtBu)(CH(2)tBu)(2)] and [( SiO)Re( CtBu)(=CHtBu)(CH(2)tBu)] to <S-z> = 0.9 for [( SiO)Mo( NAr)(=CHtBu)(R') with R' = CH(2)tBu, NPh2, NC4H4. The data also show that the motion is not isotropic and could be either a jump between two sites or more likely restricted librational motion. The dynamics are discussed in terms of the molecular structure of the surface organometallic complexes, and the orientation of the CSAs tensor at the alkylidene carbon is shown to be directly related to the magnitude of the alpha-alkylidene CH agostic interation.
000204383 700__ $$aBlanc, Frederic
000204383 700__ $$aBasset, Jean-Marie
000204383 700__ $$aCoperet, Christophe
000204383 700__ $$aSinha, Amritanshu
000204383 700__ $$aTonzetich, Zachary J.
000204383 700__ $$aSchrock, Richard R.
000204383 700__ $$aSolans-Monfort, Xavier
000204383 700__ $$aClot, Eric
000204383 700__ $$aEisenstein, Odile
000204383 700__ $$aLesage, Anne
000204383 700__ $$0248253$$aEmsley, Lyndon$$g251248
000204383 773__ $$j130$$k18$$q5886-5900$$tJOURNAL OF THE AMERICAN CHEMICAL SOCIETY
000204383 909C0 $$0252518$$pLRM$$xU12975
000204383 909CO $$ooai:infoscience.tind.io:204383$$pSB$$particle
000204383 937__ $$aEPFL-ARTICLE-204383
000204383 970__ $$aISI:000255629400027/LRM
000204383 973__ $$aOTHER$$rREVIEWED$$sPUBLISHED
000204383 980__ $$aARTICLE